The present invention relates to an ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus for use in an optical pulse generator for generating light pulses variable and multiple in wavelength over an ultra-broad bandwidth, i.e., a pulse waveform shaping apparatus for shaping light pulses variable and multiple in wavelength over an ultra-broad bandwidth, in which an ultra-broadband light pulse is produced and is then subjected to two-dimensional modulations both In amplitude and phase effected in a beam of the light pulse.
Light pulse waveform shaping has hitherto been performed by passing a light pulse having a single preselected center wavelength through either a one-dimensional spatial phase modulator or a one-dimensional spatial amplitude modulator or a combination of the two, or passing a light pulse having a single preselected center wavelength through a two-dimensional spatial phase modulator.
Light pulse waveform shaping of this type is designed to shape the waveform of a light pulse having a single preselected center wavelength by using a dispersing element to spatially expand the light pulse in dependence on its wavelengths and to effect a phase or an amplitude modulation for each of its wavelength components.
As the literature for the case of using a one-dimensional spatial phase modulator and for the case of using a one-dimensional spatial amplitude modulator, here may be cited xe2x80x9cA. M. Weiner, J. P. Heritage and E. M. Kirschner, J. Opt. Soc. Am. B5, 1563 (1988)xe2x80x9d.
Also, as the literature for the case of using both of them, here can be cited xe2x80x9cM. M. Wefers and K. A. Nelson, Opt. Lett. 18, 2032 (1993)xe2x80x9d.
Further, as the literature for the case of using a two-dimensional spatial phase modulator, here may be cited xe2x80x9cM. M. Wefers, K. A. Nelson and A. M. M. Weiners, Opt. Lett. 21, 746 (1996)xe2x80x9d.
In the instances shown in the past literature cited above, however, the use of either a one-dimensional spatial phase modulator or a one-dimensional spatial amplitude modulator or even the use of both of them permitted only light pulses of the single center wavelength shaped in waveform to be obtained.
On the other hand, the instance of using a two-dimensional spatial phase modulator made it possible to obtain light pulses varying in waveform with their spatial positions but having the same one wavelength, and thus again permitted only light pulses of the single center wavelength shaped in waveform to be obtained.
In view of the problem noted above, the present invention is aimed to provide an ultra-broadband, variable and multiple wavelength, waveform shaping apparatus that excels with the ability to yield light pulses shaped in waveform, variable and multiple in wavelength over an ultra-broad bandwidth, the pulses being as short as in the order of pico-seconds or less, or even in the order of femto-seconds.
In order to achieve the object mentioned above, the present invention provides as set forth in the appended claims an ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus, characterized in that it comprises: an ultra-broadband light pulse producing means for receiving a fundamental wave light pulse having a bandwidth and broadening the bandwidth of said fundamental wave light pulse into an ultra-broadband range to produce an ultra-broadband light pulse in the form of a beam thereof; a beam expander means comprising a cylindrical lens for expanding the cross section of the said beam of ultra-broad band light pulse in one direction (say along a y-axis) to form an expanded beam of ultra-broadband light pulse and a diffraction grating or the like for dispersing wavelengths of the ultra-broadband light pulse of the said expanded beam in a direction orthogonal to the y-axis (say in a direction of an x-axis) to produce a beam of ultra-broadband light pulse with its cross section thus expanded two-dimensionally; a two-dimensional spatial amplitude modulator for applying amplitude modulation to the said two-dimensionally expanded ultra-broadband light pulse for each, independent of another, of rows each extending in the direction (along the x-axis) of such wavelength dispersion (y-rows: y1, y2, y3 and y4) to take out thereof, light pulse components having their mutually independent center wavelengths (xcex1, xcex2, xcex3, and xcex4) for those respective rows; a two-dimensional spatial phase modulator for applying phase modulation to the said light pulse components having their mutually independent center wavelengths (xcex1, xcex2, xcex3, and xcex4) for each of such rows, independent of another; and a cylindrical lens or a cylindrical mirror and a diffraction grating or a prism for reducing, and condensing into the direction of the said x-axis, the said light pulse components modulated by the said two-dimensional spatial amplitude modulator and the said two-dimensional spatial phase modulator, whereby a plurality of pulses shaped in waveform and controlled in amplitude and phase independently for each of said center wavelengths ensue at different positions on an output screen.
In the makeup mentioned above, the ultra-broadband light pulse generating means enables a fundamental wave light pulse to bring about a self-phase modulation effect and thereby to result in an expanded spectrum, or to bring about an induced phase modulation effect between such a fundamental wave pulse and a pulse generated by a nonlinear phenomenon that takes place using the fundamental wave pulse and thereby to result in an expanded spectrum and to produce an ultra-broadband light pulse. Compared with dispersing the wavelengths of a fundamental wave light pulse, dispersing the wavelength of an ultra-broadband light pulse enables the wavelengths in an ultra-broadband that contains wavelengths in an extremely wide range to be dispersed. Applying amplitude modulations with a selected pattern to given rows, each of which extends in the direction of wavelength dispersion, in the 2-dimensional amplitude modulator to establish amplitudes permits light components with their respective, preselected center wavelengths to be cut out over the broad range of wavelengths. Also, with the ability to apply amplitude modulations to all of the rows in the 2-dimensional amplitude modulator independently of one another, it is possible to cut out light components varying in center wavelength by the number of the rows. Then, applying phase modulations with a selected pattern to the rows in the 2-dimensional phase modulator which correspond to the given rows in the 2-dimensional amplitude modulator permits a particular phase that realizes the temporal waveform of a desired particular pulse train to be added to each of those different rows, independently of one another. The beam reducing and waveform shaping means designed to reduce the beam cross section selectively in the direction of wavelength dispersion, thereby to reshape the beam allows a light pulse outgoing from the 2-dimensional phase modulator to be reduced in cross section only in the direction in which each of the rows extends, namely in the direction of wavelength, thus permitting the shaped light pulse waveforms to appear at positions on the output screen which vary corresponding to the positions of those rows.
The ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus set forth in the appended claims may, as set forth in the appended claims, further be characterized in that the said fundamental wave light pulse is an ultra-short pulse of pico-seconds or less generated by a laser light source.
The ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus set forth in the appended claims may, as set forth in the appended claims, further be characterized in that the said light source for generating the said fundamental wave light pulse is any one of a solid state laser, a fiber laser, a semiconductor laser, a dye laser and an optical parametric laser, or a combination thereof with an amplifier system.
The ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus set forth in the appended claims may, as set forth in the appended claims, further be characterized in that the said ultra-broadband high pulse producing means includes at least one nonlinear optical medium adapted for the said fundamental wave light pulse to be passed therethrough to bring about self-phase modulation and induced phase modulation effects whereby the said fundamental wave light pulse is broadened in spectrum into the said ultra-broadband range.
The ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus set forth in the appended claims may, as set forth in the appended claims, further be characterized in that the said ultra-broadband light pulse produced by the said ultra-broadband light pulse producing means is a light pulse of pico-seconds or less.
The ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus set forth in the appended claims may, as set forth in the appended claims, further be characterized in that the said nonlinear optical medium is a hollow fiber filled with either a gas or an ionized gas.
The ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus set forth in the appended claims may, as set forth in the appended claims, further be characterized in that the said nonlinear optical medium is made of any one of a waveguide structure, a bulk structure, a thin film structure, a photonic crystalline structure, a photonic fiber and a liquid, or an optical combination of two or more thereof.
The ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus set forth in the appended claims may, as set forth in the appended claims, further be characterized in that the said nonlinear optical medium has a third-order nonlinear optical property.
The ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus set forth in the appended claims may, as set forth in the appended claims, further be characterized in that the said two-dimensional spatial amplitude modulator for establishing the amplitude of the said light transmitting and the said two-dimensional spatial phase modulator for establishing its phase are arranged orthogonal to the optical axis and in series with each other and are capable of establishing the said amplitude and phase independently of each other and for each of the rows, each extending in the direction of wavelength dispersion, independently of one another.
The ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus set forth in the appended claims may, as set forth in the appended claims, further be characterized in that the said two-dimensional spatial amplitude modulator and the said two-dimensional spatial phase modulator are each subjected to a feedback control so as to provide desired pulses.
The ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus set forth in the appended claims may, as set forth in the appended claims, further be characterized in that the said two-dimensional spatial amplitude modulator comprises a first ultra-broadband polarizing plate, a two-dimensional spatial phase modulator having a plurality of pixels, and a second ultra-broadband polarizing plate to which the said first ultra-broadband polarizing plate and a polarization axis of transmission extend perpendicular.
The ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus set forth in the appended claims may, as set forth in the appended claims, further be characterized in that the said beam reducing and waveform shaping means for reducing the expanded beam cross section selectively in the direction of wavelength dispersion, thereby shaping the waveform of the light pulse, is made of a cylindrical lens or a cylindrical mirror for reducing the light beam in one direction and a diffraction grating or a prism for condensing wavelength components of the light beam reduced in the one direction, whereby a plurality of waveform shaped patterns are formed at different position of an output screen.
The apparatus as set forth in the appended claims may also be characterized in that the said nonlinear optical medium is made of any one of a waveguide structure, a bulk structure, a thin film structure, a photonic crystalline structure, a photonic fiber and a liquid, or an optical combination of two or more thereof.
The apparatus as set forth in the appended claims may also be characterized in that the said nonlinear optical medium has a third-order nonlinear optical property.
The apparatus as set forth in the appended claims may also be characterized in that the said two-dimensional spatial amplitude modulator includes a two-dimensional space filter for selecting different center amplitudes from the ultra-broadband light pulse.
The apparatus as set forth in the appended claims may also be characterized in that the said two-dimensional spatial amplitude modulator comprises a first ultra-broadband polarizing plate, a two-dimensional spatial phase modulator, and a second ultra-broadband polarizing plate of which the polarization axis is perpendicular to the polarization axis of the said first polarizing plate.
The present invention by taking a makeup as mentioned above makes it possible to produce a plurality of optical pulse trains variable and multiple in wavelength, each independently of another and simultaneously or synchronously with another.
If such light pulses variable in wavelength and shaped with waveforms as desired are used and a material is irradiated with those light pulses with controlled wavelengths adequate to cause the electron energy level resonance and controlled time intervals in such a shaped train of pulses adequate to cause the vibrational energy level resonance, it is made possible to effect what is called multi-dimensional, electron energy level and vibrational energy level dual and selective excitation, thereby to pave the way for application to the control of a chemical reaction and also to growth control.